WASHINGTON (AP) — A U.S. official said Thursday that American intelligence authorities now believe a surface-to-air missile took down the Malaysian passenger plane as it flew over eastern Ukraine.

The official said the U.S. was still working to determine additional details about the crash, including who fired the missile and whether it came from the Russian or Ukraine side of the border. But the official said U.S. intelligence assessments suggest it is more likely pro-Russian separatists or the Russians rather than Ukrainian government forces shot down the plane.

The official was not authorized to discuss the matter publicly so spoke on condition of anonymity.

The U.S. has sophisticated technologies that can detect missile launches, including the identification of heat from the rocket engine.

The plane was carrying 295 people. The Ukraine government and pro-Russian separatists who are fighting in that region have both denied responsibility for the strike.

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